The present invention relates generally to printing systems and, more particularly to a system and method for printing on a continuous web print medium.
A conventional inkjet printing system includes a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other.
In one arrangement, commonly referred to as a fixed, wide-array inkjet printing system, a plurality of individual printheads, also referred to as printhead dies, are arranged in a staggered configuration to form a printhead array which spans a nominal page width of the print medium. In addition, the printheads are fixed or held stationary relative to the print medium as the print medium is advanced during printing. With the printhead array, a number of nozzles and, therefore, an overall number of ink drops which can be ejected per second is increased. Since the overall number of drops which can be ejected per second is increased, printing speed can be increased with the wide-array inkjet printing system.
One use of the fixed, wide-array inkjet printing system is for printing on a continuous form or continuous web print medium which includes a continuous roll and/or plurality of contiguous print medium portions each representing, for example, individual sheets, forms, labels, etc. Typically, the electronic controller resets and re-initiates operation of the entire printhead array each time the printing system detects the top of one of the print medium portions.
Unfortunately, if the conventional wide-array inkjet printing system detects a subsequent print medium portion when the printing system is currently printing an image on a preceding print medium portion, the image being printed is truncated. More specifically, when the printing system detects the subsequent print medium portion, the entire printhead array is logically reset. Thus, existing or current operation of the printhead array is terminated. Those portions yet to be printed of the image currently being printed by the printing system, therefore, are not completed. More specifically, conventional inkjet printing systems cannot simultaneously initiate printing of a subsequent image and finishing the printing of a preceding image. As such, it is necessary to leave large spaces of non-printable areas of print medium between images. Thus, the margins surrounding each image printed on the print medium are undesirably large. Consequently, printing throughput is not optimized.
One attempt to prevent such image truncation is to detect only the first print medium portion and print all subsequent images relative to the first print medium portion. A disadvantage of this approach, however, is that during the course of a print run, positions of the images have a tendency to drift relative to a respective one of the print medium portions.
Accordingly, a need exists for preventing truncation of an image when printing on a continuous web print medium with a fixed, wide-array inkjet printing system. In particular, a need exists for controlling operation of the printheads of the printing system such that printheads that are printing an image continue printing the image when the printing system is triggered to print a subsequent image.
One aspect of the present invention provides an inkjet printing system adapted to print on a print medium having a top-of-form (TOF) indicator. The inkjet printing system includes a printhead assembly, a top-of-form (TOF) detector adapted to detect the TOF indicator of the print medium, a positional sensor adapted to sense a relative position of the print medium to the printhead assembly, and a controller associated with the printhead assembly, the TOF detector, and the positional sensor. The printhead assembly includes a first printhead subarray and a second printhead subarray offset from the first printhead subarray such that the controller is configured to initiate operation of the first printhead subarray after the TOF detector detects the TOF indicator and initiate operation of the second printhead subarray at a predetermined interval after the TOF detector detects the TOF indicator. As such, the predetermined interval is related to the relative position of the print medium.
Another aspect of the present invention provides a method of printing on a print medium with an inkjet printhead assembly. The print medium has a top-of-form (TOF) indicator and the inkjet printhead assembly includes a first printhead subarray and a second printhead subarray offset from the first printhead subarray. As such, the method includes detecting the TOF indicator, initiating operation of the first printhead subarray after detecting the TOF indicator, sensing a position of the print medium relative to the inkjet printhead assembly after detecting the TOF indicator, and initiating operation of the second printhead subarray based on the position of the print medium after detecting the TOF indicator.